1. Field of the Invention
This invention relates to an image forming device which includes an intermediate transfer drive motor which rotates an intermediate transfer belt, and a secondary transfer motor which rotates a secondary transfer roller, and relates to a semiconductor device for use in an image forming device.
2. Description of the Related Art
In an image forming device, when a toner image, primarily transferred from a photoconductor drum to an intermediate transfer belt, is secondarily transferred to a recording sheet, the toner image on the intermediate transfer belt is transferred to the recording sheet by nipping the recording sheet between the intermediate transfer belt and a secondary transfer roller which are pressed against each other.
FIG. 1 shows a secondary transfer roller and an intermediate transfer belt in an image forming device. The image forming device 10 shown in FIG. 1 includes a secondary transfer roller 11, an intermediate transfer driving roller 12, a repulsive-force roller 13, an intermediate transfer belt 14, and an intermediate transfer drive motor 15.
The intermediate transfer driving roller 12 is a roller which drives the intermediate transfer belt 14, and the intermediate transfer drive motor 15 is a motor which rotates the intermediate transfer driving roller 12.
The secondary transfer roller 11 is a roller for transferring a toner image from the intermediate transfer belt 14 to a recording sheet.
The intermediate transfer belt 14 is supported by the intermediate transfer driving roller 12, the repulsive-force roller 13, and other rollers. The intermediate transfer belt 14 is driven in the direction, indicated by the arrow 16 in FIG. 1, when the intermediate transfer driving roller 12 is rotated by the intermediate transfer drive motor 15.
In the image forming device 10, the secondary transfer roller 11 and the repulsive-force roller 13, arranged in the position facing the secondary transfer roller 11, are pressed against each other, so that the intermediate transfer belt 14, supported by the repulsive-force roller 13 and the secondary transfer roller 11 are pressed against each other to nip a recording sheet 17 between them during transport.
The toner image primarily transferred from the photoconductor drum 18 to the intermediate transfer belt 14 is secondarily transferred to the recording sheet 17 when the recording sheet 17 is nipped between the secondary transfer roller 11 and the intermediate transfer belt 14 which are pressed against each other.
In order to prevent a positional deviation of a reproduced image, it is necessary that a peripheral speed of the secondary transfer roller 11 and a surface speed of the intermediate transfer belt 14 when transferring a toner image to the recording sheet 17 are in agreement with good accuracy.
However, the surface speed of the intermediate transfer belt 14 in the image forming device 10 shown in FIG. 1 may be changed by the influences of various neighboring mechanisms, such as rollers for supporting photoconductor drums 18 and rollers for supporting the recording sheet 17.
Moreover, the peripheral speed of the secondary transfer roller 11 may be changed in accordance with other factors, such as thermal expansion of the rollers at ambient temperature. If a speed difference between the peripheral speed of the secondary transfer roller 11 and the surface speed of the intermediate transfer belt 14 arises, the toner image on the intermediate transfer belt 14 is not correctly transferred to the recording sheet 17, which causes deterioration of the quality of a reproduced image, such as a color deviation.
In order to eliminate the speed difference, Japanese Laid-Open Patent Application No. 11-052757 discloses a color image forming device which uses a torque limiter to reduce fluctuations of the intermediate transfer belt speed and prevent the toner image formation positions from deviating from each other.
The torque limiter in the above-mentioned image forming device as disclosed in Japanese Laid-Open Patent Application No. 11-052757 is a mechanical part, and the life thereof is restricted. Installing the torque limiter in the image forming device also causes the cost to increase.